ath6kl: Find ar->max_norm_iface in firmware IE parsing

Currently the max number of vifs which can be used for non-p2p
mode is determined in ath6kl_core_alloc(). But the maximum
supported vifs are parsed from firmware IE in ath6kl_fetch_fw_api2()
which would happen after ath6kl_core_alloc().

Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>